<!DOCTYPE html>
<html lang="zh">
<head>
	<meta charset="UTF-8">
	<meta name="viewport"
	      content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
	<meta http-equiv="X-UA-Compatible" content="ie=edge">
	<title>Title</title>
	<style>
		.container{
			height: 800px;
			width: 800px;
			border: 1px solid salmon;
			display: flex;
		}
		.box{
			margin-right: 10px;
			width: 100px;
			height: 100px;
			border:1px solid #3eaf7c;
			cursor: pointer;
			position: relative;
		}
		.box div{
			margin-left: 80px;
		}
		.box:hover::after{
			content: '';
      background: #3eaf7c;
			height: 100px;
			position: absolute;
			left: 0;
			top: 0;
			width: 5px;
			border-radius: 4px;
		}
	</style>
</head>
<body>
 <div class="container">
	 <div class="box">
		 <div>1</div>
		 <div>2</div>
		 <div>3</div>
		 <div>4</div>
	 </div>
	 <div class="box"></div>
	 <div class="box"></div>
	 <div class="box"></div>
	 <div class="box"></div>
 </div>
</body>
</html>
